A spokeswoman with Houston-based EOG Resources Inc. said it is too early to tell what caused the explosion, and the company is working with a fire suppression crew out of Houston to contain the blaze.

"EOG is assembling well control experts and specialized equipment to safely control the well and extinguish the fire," said K Leonard, EOG public relations manager. "The company's priorities remain constant: protect the safety of those responding to the incident, neighbors in the area and the environment."

There are no reports of injuries as a result of the incident, and Leonard said all rig personnel have been safely accounted for.

However, the company has not been notified by the contract firms, who had workers on site at the time, if there have been any injuries among their workers resulting from the incident, Leonard wrote in an email Thursday afternoon.

Those living near the well site were evacuated from their homes after the blast, but only two households within a quarter-mile of the dig site are still not allowed on their property, said Yoakum Fire Department Chief Mark Herchek.

EOG is covering living expenses for its nearby neighbors who were asked to evacuate as a safety precaution during this incident.

The U.S. Department of Labor's Occupational Safety and Health Administration has cited Nabors Drilling USA, the owners of the drill site, with numerous violations for exposing workers to safety and health hazards at two oil rig drilling sites in Texas, according to a May 2012 OSHA news release.

Violations include failure to follow manufacturer's safety requirements and failure to ensure the proper use of electrical equipment.

Looking back, Marshall said there were a lot of warning signs that something was not right at the digging site.

Marshall claims that concrete did not have adequate time to dry, and a superior commanded him to go into the oil rig's cellar to tighten the bolts while it was flooding and filling with gas from the blowout that occurred earlier.

Marshall said after the incident that he learned the concrete dried for only about an hour. The process should take between four and six hours, he said.

"If I would have gone down there, I would have drowned or been hit by the gas," Marshall said.

Terry Clawson, with the media relations office for the Texas Commission on Environmental Quality, said its assistance was not requested, but TCEQ is sending staff out to the area to do some off-site air monitoring.

OSHA also will investigate Wednesday's explosion, said media relations officer Diana Petterson, adding that an inspection history of the Nabors rig F38 was not available.